Process gas chromatograph analyzer

ABSTRACT

A chromatograph testing system with a plural filament thermal conductivity detector, a pressure detector safety device in one embodiment for protecting the detector filament, and improved means for maintaining constant testing temperatures. The system is designed to reach test temperatures up to 500*F., to be compact, and to be easily maintained.

Oct. 7, 1975 United States Patent [191 Tinklepaugh et al.

XXX 33 ZZ HCR //3 in 77 22 3 33 22 Atwood et al, Heaton Dodd et al,Gaylemm. Luckey R E: in mm m n Primary Examiner-Robert M. Reese g -B: nOil omp ny f Pennsylvania. Attorney. Agent, or FirmGe0rge L. Church;Donald Philade phi PH- R. Johnson; Gary V, Pack Dec. 2, 1974 [22] Filed:

Appl, No.1528,755

A chromatograph testing system with a plural filament thermalconductivity detector, at pressure detector safety device in oneembodiment for protecting the detector filament, and improved means formaintaining constant testing temperatures. The system is de signed toreach test temperatures up to 500F, to be compact, and to be easilymaintained.

8 6 m lw w Z 7 6 |11R-:5 0 C5 G4 4 5 5& 2 am n 4 .2 u 52 NR3 H 3 02 v MGWU H .m2 WWh R H c U HE mi s .2... l 2 C 0 S UhF Z QM S5 J 6] ReferencesCited 6 Claims, 6 Drawing Figures m 2 N 7 S N E T. Am M Sm m s mm D l W%NH U7 7 4 m 9 2 US. Patent 0a. 7,1975 Sheet 2 of3 PROCESS GASCHROMATOGRAPH ANALYZER The control valve and actuating mechanismdisclosed herein is disclosed and claimed in a copending application,Ser. No. 528,756, filed of even date herewith.

This invention relates to gas chromatography, and more particularly to adesign for a gas chromatograph which increases the accuracy andreliability of test results and decreases the time required formaintenance and repair.

One major concern in industry is to have its processes in continuousoperation to assure maximum output. The gas chromatograph is often usedas a monitor on many processes in a refinery or other industrialsettings. A major problem develops when these chromatographs fail tooperate properly because of the length of time required for repair. Thisinvention discloses a design which features modularization of eachcomponent so that when part of the chromatograph stops operating, it canbe easily replaced and the defective component can be returned to a shopfor repair and analysis of the reason for failure.

All elements of this invention are designed for easy and quickreplacement in the field of operation. The tubing for the columnseparator is wound tightly around a ring. thereby allowing replacementof a co' umn by merely disconnecting the two ends of the columnseparator tube and slipping the ring off of the heating block. Eachdetector filament is secured in a socket. thereby facilitating easyreplacement. The ease of replacing the other components will becomeevident in the detailed description of this invention.

Several design features in the chromatograph help assure maximumaccuracy in the test results. An essentially solid metal heating blockhouses the detector filaments. The mass of the metal comprising theheating block acts as a heat sink. maintaining a constant uniformtemperature for the columns and detector components. This constanttemperature provides more accu rate test results which can easily beplotted as a bar graph. These bar graphs have improved peak shapes thatcan be read by the process operator much easier than the conventionaltriangular plots.

An object of this invention is to improve a simple de sign for a gaschromatograph with easily interchangeable components.

Another object of this invention is to provide a gas chromatograph withthe capability of maintaining constant temperature control of the samplegas and the detector components.

Another object of this invention is to provide a safety device to detectpressure losses in the chromatograph and to turn off the detectorelements in the event of loss of pressure thereby preventing theirburnout.

A still further object of this invention is to provide a gaschromatograph which can reach test temperatures to 500 and be able tosustain continuous testing at these high temperatures.

The objects of this invention are accomplished briefly in the followingmanner: A generally cylindrical metal heating block, housing a cartridgeheater and the detector filaments, is maintained at the testingtemperature desired. The columns are affixed around the heating block tobe maintained at a constant operating temperature. A fourteen-portrotary control valve designed to withstand the high testing temperaturesdesired is used to provide all the switching and sampling requirements.A pair of steel bellows is used to actuate the rotary valve.

Further objects and advantages of this invention will become obvious inthe following detailed description of the invention, taken inconjunction with the accompanying drawings, wherein:

FIG. I is a front view of the invention disclosed without the ovencover.

FIG. 2 is a top view of the invention with the heating block andadjoining components removed.

FIG. 3 is a sectional view of the heating block taken along line 33 ofFIG. 1.

FIG. 4 is a sectional view of the heating block taken along line 44 inFIG. 1.

FIG. 5 is a sectional view of the heating block taken along line S5 inFIG. 1.

FIG. 6 is a flow diagram of the gas chromatography system in thisinvention.

Refer now to the figures provided. The entire chromatograph with theexception of its electronic controls is contained in an oven which isinsulated on all sides. The top and the four sides are constructed asone sec tion (not shown) which rests tightly against the oven base 12.

Heating plate 13 rests on oven base 12 and is secured thereto by bolts14. Embedded in heating plate I3 is heating element I5. Temperaturesensor I6 and heat limiter switch 17 rest in passages embedded inheating plate 13. Resting on the upper surface area of heating plate 13is the tubing for heat transfer coil 18.

FIGS. I and 2 illustrate one possible valve and valve actuation design.Control valve housing frame 21 is so cured by screws 22 to the uppersurface of heating plate 13. Steel bellows 23 and 24 are mounted on oneside of housing frame 21. Openings on housing frame 21 at the locationwhere each steel bellows. 23 or 24 is mounted, allow for connection ofsteel bellows 23 and 24 to a pressure source (not shown) for actuationthrough tubing 25 and 26 and couplings 27 and 28 respectively. Rotarycontrol valve 29 is securely mounted to the top side of housing frame 21with valve drive shaft 31 of control valve 29 extending through opening(not shown) in the top side of housing frame 21. Drive shaft 31 isconnected securely to the center of lever 33. One end of lever 33 isconnected pivotally to push rod 34 of steel bellows 23 by pivot pin 35and the other end of lever 33 is pivotally connected to push rod 36 ofsteel bellows 24 by pivot pin 37. Stop blocks 38 and 39 are secured tothe side of housing frame 21 opposite steel bellows 23 and 24,respectively. The conduit connections to control valve 29, with theexception of heat transfer 18, are omitted from FIGS. 1 and 2 sincethese connections vary with the testing sequence used.

Rigid support pipe 40 passes through and is secured to heating plate I3.Explosion proof housing 41 is threadedly secured to and supported bysupport pipe 40. Heating block 42 is thrcadedly engaged to housing 41.Heating block 42, which serves as the body for thcrmal conductivitydetector 58 (FIG. 6), is essentially solid with the exception of severalchannels. Cylindrical channel 43 spans the entire longitudinal axis ofheating block 42, housing heating element 44. Stop plug 45 is threadedlyengaged in the external end of channel 43. Four longitudinal filamentchambers. 46 and 46'. of equal size are bored in the internal end ofheating block 42. For clarity, only filament chamber 46 is shown in FIG.3. A plug 47 is threaded into each filament chamber 46 and 46' in such amanner as to seal each filament chamber. Each plug 47 seals a detectorfilament 48 inside its respective chamber, having the detector filamentelectrical leads 73 pass through the plug itself. Four internalpassages, 49 and 49', lead from the outside wall of heating block 42 atcoupling 50 and 50', to their respective sealed longitudinal filamentchamber 46, or 46', as seen in FIG. 4. Two inter' nal connectingpassages, 51, connect filament chambers 46 to filament chambers 46 asshown in FIG. 5. Plugs 52 block the external end of each connectingpassage 51. When the chromatograph is in operation, two streams of gaspass through the above passages. For example, carrier gas enterscoupling 50, flows through internal passage 49 into filament chamber 46,through connecting passage 51 into filament chamber 46 and then flowsout of heating block 42 by way of internal passage 49' and coupling 50'.The same flow pattern is followed for the other symmetrical combinationof passages and sealed chambers.

A longitudinal opening 53 houses temperature sensor 54 and otherlongitudinal opening 55 houses heat limiter switch (not shown).

All the aforementioned electrical components housed in heating block 42are placed in their respective opening in such a manner that theirterminals run outside of heating block 42, but inside explosion proofhousing 4] and can be connected to wires which run through the inside ofsupport pipe 40 to electronic control systems (not shown) outside theoven. Explosion proof housing 41 has a housing cap 56 which isthreadedly attached and can easily be removed for easy ac cess to theelectrical connections contained therein.

The column separator 60, which typically comprises two columns arrangedfor series flow, is wound tightly around a generally cylindricalstructure ring 61 and held firmly in place by clamping members 62 whichare attached to structure ring 61 by screws 63. For operation, structurering 61 is slid over the external end of heating block 42 and the endsof the tubing of column separator are coupled to the appropriate portsof control valve 29. In the center of heater block 42, capillary tubing64 is wrapped tightly around the circumference of heating block 42 andheld in place firmly by support members 65, which are secured to heatingblock 42 by screws 66.

For normal operations an electronic control system is needed to operatethe chromatograph. Separate control systems that are connected totemperature sensors 16 and 54 are used to maintain the correcttemperature in heating plate 13 and heating block 42. The heat limitingswitches act as a fuse by turning off the heat if the temperature risesabove a certain point. A timing system is needed for activating controlvalve 29. Electronic circuits above described are available and known tothose skilled in the art and constitute no part of this invention.

There is no one preferred use of the design above described. Because ofthe versatility of the design and rotary valve used, several differenttypes of tests can be set up. Adjustments for a different test aresimple. The only changes needed are to switch the connections to therotary valve, thereby changing the paths in which the tdst sample andcarrier gas flow through. Generally, in many tests, the followingsequence for sample and carrier gas flow takes place. Referring to FIG.6, the sample enters the oven enclosure and passes through LII heattransfer coil 18 in which the sample temperature is raised to theoperating temperature of the chromatograph. The sample then flows tocontrol valve 29. In the normal mode of operation the sample fluidpasses through control valve 29. For sampling, control valve 29 rotatesquickly, catching small quantity of sample fluid in the control valve.This quantity of sample fluid is carried out of control valve 29 by thecarrier gas and to a column separator. If the sample is a liquid, onceit is inserted into the chromatograph system, it vaporizes because ofits reduced partial pressure. Next, the sample is separated into itscomponents by flowing through column separators 60. The number andsequence of column separators and direction of flow through the columnsdepend on the test. The separated sample next flows through controlvalve 29 and to heating block 42 of detector 58. By way of internalpassage 49, the sepa rated sample and the carrier gas pass through thefilament chamber housing detector filament 48. The separated samplecontinues to flow through heating block 42 by way of connecting passage51 and into another filament chamber 46' housing a detector filament(not shown), eventually exiting heating block 42 through internalpassage 49'. The separated sample is carried by the carrier gas to apressure switch or a flow measurement device and then vented into theoutside air. When the pressure switch detects a loss in line pressure orthe flow measurement device detects a drop in the flow rate, the powerto detector 58 is turned off to avoid burning out the detector filaments48.

The carrier gas, such as helium for example, serves to push the samplegas throughout the entire test. The carrier gas enters the oven andflows through capillary tubes 64. The capillary tubes serve to provide aconstant rate of flow of carrier gas, thereby resulting in more accuratetest data. The carrier gas then passes through heating block 42 ofdetector 58, flowing through two different detector filaments exactly asexplained for the separated sample and the carrier gas. The carrier gasthen enters the control valve where it can be channeled to clean out thecolumn separators between tests or carry the sample gas during tests.

Since the usual variations in the flow pattern relate to control valve29 connections, no specific flow pattern through valve 29 is indicatedin the diagram. Examples of flow patterns through the control valve canbe found in Young, US. Pat. No. 3,223,123.

Actuation of control valve 29 is by carrier gas pressure applied to oneof the steel bellows 23 or 24. A solenoid valve 71, activated by a timer(not shown switches the carrier gas pressure between each steel bellows.Normally, one steel bellows is in the expanded position, its push rodfully extended against its respective stop block, and the other steelbellows remains in its rest or deflated position. When the timerswitches the solenoid, the solenoid changes the carrier gas pressure tothe other steel bellows and returns to its original position after thesample gas has had sufficient time to be carried through the detectorfilaments by the carrier gas.

The chromatograph reading is determined with a conventional wheatstonebridge arrangement using the four detector filaments 48. However, a twofilament wheatstone bridge can be used by replacing two of the filamentswith fixed resistors. Various kinds of detector filaments can be used inthe thermal conductivity detector, including thermistor and catalyticfilaments.

Heater block 42 helps assure constant temperature of the gas when itenters the filament chambers, and prevents minute temperature changeswhich alter the resistivity of the detector filaments, thereby affectingthe test results. Heating plate 13 heats the air in the oven in order tohelp assure a constant temperature in heating block 42. Heating plate 13also controls the temperature of control valve 29 as well as the samplegas flowing through the chromatograph. Control valve 29 provides quickand accurate sample volumes. Small diameter columns and small samplevolumes decrease the time for testing, which results in improved peakshapes of the test data. Because of the accuracy of the resultsobtained, accurate bar graphs can be plotted from the tests. This typeof graph is much easier and much more accurate to read as compared tothe conventional triangular shaped graph.

The design features also permit easy replacement of any part in thefield avoiding long shutdown times or replacement of entire units.

This invention is particularly adaptable to use in remote areas. Regularhousehold current is sufficient for the electrical requirements and thecarrier gas also provides the pressure required for steel bellows 23 and24 to actuate control valve 29. Low current lines of VDC or less areless susceptible to noise pickup over long distances and can be used tocontrol the tests in many chromatographs from one central location.

From the above disclosure, it can be seen that there has been provided agas chromatograph having a novel and improved design which combines theelements of the chromatograph in such a manner as to provide veryconstant test temperatures which permit accurate and reliable test datato be recorded. Also included in this design are features which allowquick and easy replacement of any part of the gas chromatograph.

The invention claimed is:

1. In a gas chromatography apparatus, a means for achieving moreaccurate test data by reducing temperature variations within thechromatograph components, comprising:

a. an insulated container,

b. an essentially solid heating block, having a plurality of internalpassages and mounted inside the insulated container.

c7 a plurality of detector filaments embedded in the heating block, saidinternal passages providing fluid communication from the exterior of theheating block to the detector filaments,

d. heating means embedded in the heating block, and

e. tubing wound around the circumference of the heating block for use ascolumn separators.

2. Apparatus claimed in claim 1 whereby the plurality of tubes areconnected to the circumference of the 6 heating block by meanscomprising:

a. an annular ring with a size and shape that allows the ring to fitsnugly around the circumference of the heating block, b. a plurality oftubes wound tightly around the annular ring, and c. means for securingthe tubes to the ring. 3. Apparatus claimed in claim 1 which includes ameans for heating the air surrounding the heating block as well as thesample gas, comprising:

a. an essentially solid metal heating plate, and b. heating meansembedded in the heating plate. 4. In a gas chromatography apparatus, athermal conductivity detector designed to maintain a constanttemperature, comprising:

a. an insulated container, b. an essentially solid cylindrical heatingblock, having a plurality of internal chambers and passages and mountedinside the insulated container, 0. a plurality of detector filaments, d.a plurality of insulated plugs, holding their respective detectorfilament securely in each respective internal chamber ofthe heatingblock, said internal passages providing fluid communication from theexterior of the heating block to the detector fila merits and betweenthe detector filaments, e. a means for heating the heating block andmaintaining a constant preset temperature, comprising: i. an elongatedheating element resting in an inter nal chamber spanning thelongitudinal axis ofthe heating block, and

ii. means to detect the temperature of the heating block and forchanging the temperature in the heating element as required, and

. a plurality of tubes wound tightly around the cir cumference of theheating block for use column separators and carrier gas flow control.

5. Apparatus claimed in claim 4, which includes a means for preventingburnout of the detector filaments comprising:

a pressure switch mounted in the chromatograph downstream from thedetector, so installed that the power to the detector is switched offwhen the pressure in the chromatograph drops below a predeterminedamount.

6. Apparatus claimed in claim 5 where said means for preventing burnoutof the detector filaments com prises:

a flow measurement device downstream from the de tector, so installedthat the power to the detector is switched off when the flow rate in thechromatoan H... "hm. M

1. IN A GAS CHROMATOGRAPHY APPARATUS, A MEANS FOR ACHIEVING MOREACCURATE TEST DATA BY REDUCING TEMPERATURE VARIATIONS WITHIN THECHROMATOGRAPH COMPONENTS, COMPRISING: A. AN INSULATED CONTAINER, B. ANESSENTIALLY SOLID HEATING BLOCK, HAVING PLURALITY OF INTERNAL PASSAGESMOUNTED INSIDE THE INSULATED CON TAINER, C. A PLURALITY OF DETECTORFILAMENTS EMBEDDED IN THE HEATING BLOCK, SAID INTERNAL PASSAGESPROVIDING FLUID COMMUNICATION FROM THE EXTERIOR OF THE HEATING BLOCK TOTHE DECTOR FILAMENTS, D. HEATING MEANS EMBEDDED IN THE HEATING BLOCK,AND E. TUBING WOUND AROUND THE CIRCUMFERENCE OF THE HEATING BLOCK FORUSE AS COLUMN SEPARTORS.
 2. Apparatus claimed in claim 1 whereby theplurality of tubes are connected to the circumference of the heatingblock by means comprising: a. an annular ring with a size and shape thatallows the ring to fit snugly around the circumference of the heatingblock, b. a plurality of tubes wound tightly around the annular ring,and c. means for securing the tubes to the ring.
 3. Apparatus claimed inclaim 1 which includes a means for heating the air surrounding theheating block as well as the sample gas, comprising: a. an essentiallysolid metal heating plate, and b. heating means embedded in the heatingplate.
 4. In a gas chromatography apparatus, a thermal conductivitydetector designed to maintain a constant temperature, comprising: a. aninsulated container, b. an essentially solid cylindrical heating block,having a plurality of internal chambers and passages and mounted insidethe insulated container, c. a plurality of detector filaments, d. aplurality of insulated plugs, holding their respective detector filamentsecurely in each respective internal chamber of the heating block, saidinternal passages providing fluid communication from the exterior of theheating block to the detector filaments and between the detectorfilaments, e. a means for heating the heating block and maintaining aconstant preset temperature, comprising: i. an elongated heating elementresting in an internal chamber spanning the longitudinal axis of theheating block, and ii. means to detect the temperature of the heatingblock and for changing the temperature in the heating element asrequired, and f. a plurality of tubes wound tightly around thecircumference of the heating block for use as column separators andcarrier gas flow control.
 5. Apparatus claimed in claim 4, whichincludes a means for preventing burnout of the detector filamentscomprising: a pressure switch mounted in the chromatograph downstreamfrom the detector, so installed that the power to the detector isswitched off when the pressure in the chromatograph drops below apredetermined amount.
 6. Apparatus claimed in claim 5 where said meansfor preventing burnout of the detector filaments comprises: a flowmeasurement device downstream from the detector, so installed that thepower to tHe detector is switched off when the flow rate in thechromatograph drops below a predetermined amount.